1. Field of the Invention
The present invention relates to a passive seat belt system equipped in a vehicle such as an automotive vehicle in order to restrain the breast section of a passenger of the vehicle, and more particularly to a passive seat belt system configurated such that a webbing for restraining the passenger is driven by a webbing driving device in response to opening and closing states of a vehicle door, in which the webbing driving device is made inoperative when impact is applied to the vehicle.
2. Description of the Prior Art
A variety of passive seat belt systems have been proposed and put into practical use. A typical conventional system is disclosed in Japanese Patent Provisional Publication No. 56-71643 in which a passive seat belt system including a webbing for restraining a passenger is driven by a webbing driving means which is controlled in response to opening and closing states of a vehicle door. Impact detecting means is provided to detect impact applied to a vehicle to output an impact signal. The impact signal is maintained for a predetermined time under the action of a timer. Additionally, a driving prohibition commanding means is provided to make the webbing driving means inoperative during a predetermined time in which the impact signal is maintained by the timer. Thus, according to the above-described conventional passive seat belt system, within the predetermined time after impact is detected by the impact detecting means, the webbing driving means is made inoperative even when the vehicle door is opened, thereby preventing the webbing from being driven in the direction of releasing the passenger even in a condition in which the vehicle door is opened by impact at vehicle collision.
However, difficulties have been encountered in the conventional passive seat belt system in that the passenger cannot make an emergency vehicle escape action even upon opening of the vehicle door immediately after the impact detecting means detects impact when a sudden stop of the vehicle is made upon applying sudden brake or the like, because the conventional passive seat belt system is arranged so that the webbing driving means is necessarily made inoperative for the predetermined time under the action of a timer and the driving prohibition commanding means in response to the impact signal from the impact detecting means.